1. Field of the Invention
This invention relates to internal combustion engines for automotive vehicles and, more particularly, to methods and means for controlling the flow of fuel through the idle jet of a carburetor. More particularly, this invention is concerned with improving the fuel economy of automotive vehicles by stopping the flow of fuel through the idle jet of the carburetor of an internal combustion engine when idle jet fuel is not required to keep the engine running.
2. Description of the Prior Art
To prevent an internal combustion engine from stalling when the throttle (butterfly valve of the carburetor) is closed, it is conventional to provide an idle jet on the intake manifold side of the butterfly valve to provide fuel to keep the engine idling. It has long been recognized that the idle jet wastes gas since fuel continues to flow through it without regard as to whether fuel is needed to keep the engine idling. A particularly wasteful condition occurs when the vehicle is coasting downhill or into a controlled intersection. Here the operator's foot is off the throttle but, due to the speed of the coasting vehicle and the fact that the butterfly valve is shut, the vacuum within the intake manifold rises toward a maximum and raw fuel is drawn through the idle jet and into the engine at a high rate. Since the vehicle is coasting, no fuel is needed to keep the engine running and the fuel that is fed through the idle jet is totally wasted. This is not only wasteful but is also undesirable since there is not enough combustion air to burn the raw fuel that passes through the idle jet resulting in an engine exhaust high in unburned hydrocarbons and other objectionable emissions.
Prior art devices have proposed solutions to this problem by providing valved means to discontinue the flow of fuel through the idle jet of the carburetor when the vacuum in the intake manifold is high since this is the condition that pertains when the operator's foot is off the throttle when the vehicle is coasting. While these devices are theoretically sound, they generally fail in practice since the engine will stall when the vehicle decelerates to a low speed even though the vacuum is still high. Also these devices variously may be complex and expensive, or not readily useable in modifying existing carburetors.